High level of arsenic in groundwater has affected 120,000 people in 12 Bihar districts, including capital Patna, says the state's Public Health and Engineering Department Minister Prem Kumar.
Drinking water with high arsenic content may cause life-threatening diseases like gangrene, cancer of the intestines, liver, kidneys and the bladder.
"High level of arsenic in the groundwater is posing a threat to 120,000 people living along the Ganga," Prem Kumar told IANS after he apprised the state assembly of the danger.
He said the worst affected district was Bhojpur, followed by Buxar, Vaishali, Bhagalpur, Samastipur, Khagaria, Katihar, Chapra, Munger and Darbhanga.
Harail Chapar, a village in Samastipur district, recorded 2,100 parts per billion (ppb) of arsenic in groundwater, the highest in the state.
The World Health Organisation guideline for a safe limit is 10 ppb, while the Indian government's guideline is 50 ppb.
The 12 districts under threat were identified in a state government report prepared last year on the basis of a survey that collected water samples at random from 19,961 tubewells in 398 villages, spread across 42 blocks in 12 districts.
The survey found that arsenic concentration in the samples was above 10 ppb in 310 villages and above 50 ppb in 235 villages.
"It appears that all the 12 districts situated by the side of river Ganga are highly arsenic contaminated," the survey report said.
Kumar said the government "is making available pure drinking water to the people in the affected areas and was conducting a study to find out why the concentration of arsenic was so high in the groundwater."
The government has commissioned a water treatment project estimated at Rs.539 million in Bhojpur district. "The clean treated water from river Ganga will be supplied to the affected villages," he said.
Besides, the existing wells in the affected villages have been cleaned up to supply potable water to the people.
Arsenic, an odourless and tasteless semi-metallic element, occurs naturally in the environment. The concentration increases due to agricultural and industrial activity.